text:
Why do some fighter jets have movable horizontal stabilizer instead of elevators installed on the stabilizers?
I have noticed that the horizontal stabilizers on some fighter jets move up and down to increase and decrease the angle of attack, but on some airliners they use elevators to adjust the angle of attack. Why isn't this kind of system used on airliners?

Not all fighters use moving stabilsers.  Not all airliners use elevators.  You might be better rephrasing the question?

Peter Kampf's answer (as usual) is correct. However, I'd like to stress the first point he makes about the benefits of full-flying tail surfaces: the full-flying stabilizer was a solution to loss-of-control issues (google "compressibility problem") when airplanes enter transonic and supersonic speeds. Civilian planes don't go supersonic and so can use the cheaper elevators.

All parts of an airliner's horizontal surface move, not just the rear part. The rear part, called an elevator, can move much faster and is for maneuvering. The forward part, called a (trimmable) stabilizer, is for trimming and moves slowly. It is moved in response to changes in loading, speed or flap settings and positions the tail surface such that only small continuous elevator deflections are needed. It doesn't need to move fast - high load factors would upset the passengers and overload the structure.

A330 port tailplane root (picture source). Note the markings which show the range of incidence angles covered by the trimmable stabilizer.
Benefits of a stabilizer-elevator configuration:

Camber: The elevator deflection changes the camber of the airfoil of the tail surface and makes the production of the intended lift change more efficient. If the elevator deflection is supposed to create a downforce, negative camber is produced and vice versa. This reduces the drag which is created in order to maneuver the aircraft.
Lower control forces: By moving a smaller surface, less hydraulics power, and on small aircraft, less muscle power is needed for the same moment change than with a full-flying tail or all-moving surface. Makes sense, right?
Better tailoring of the hinge moment derivatives: Two effects are important for getting the control forces right: The change in hinge moment over deflection angle ($c_{r\eta}$), and the change in hinge moment over angle of attack ($c_{r\alpha}$). With tabs, the right elevator hinge position, nose shape and control horns, both can be tailored individually, while a full-flying tail or all-moving surface will give the designer less freedom to manipulate both independently. Note that full-flying tails only emerged with hydraulic controls, because only those systems can manage the control forces of all-moving control surfaces at high speed.

Horn balance and overhang balance on control surfaces (picture source)
Benefits of a full-flying tail surface

By avoiding a contour break due to a flap deflection, all-moving control surfaces can avoid the shocks which would otherwise occur at high subsonic speed. This is their main benefit for combat aircraft.
At supersonic speed, the uncambered surface will produce less drag, so for supersonic speed the all-moving control surface is more efficient.
By moving all of the tail surface at high speed, an all-moving control surface will produce the highest rate of moment change over time possible. To produce also the highest sustained moment change, however, it needs to be larger than a comparable stabilizer-elevator combination because it forfeits the benefits of variable camber.
The all-moving control surface has no gaps which could add radar reflections, allowing for a more stealthy design.
Lower mechanical complexity. This is somewhat offset by the need for much beefier hydraulics.

The all movable horizontal tailplane is usually called a stabilator (stabilizer + elevator) or all moving tail plane or in some cases tail slab. This is mostly used in combat aircraft for a few reasons:

Enhanced Maneuverability. The all moving tailplane offers higher maneuverability compared to the stabilizer + elevator found in civil aircraft. Basically, the stabilator gives wider range of pitch control over a larger range of speeds. Also, the stabilator is also hinged about the aerodynamic center, requiring comparatively lesser control input from the pilot for operation.

"F 22 Raptor Tail Feathers photo D Ramey Logan" by WPPilot - Own work. Licensed under CC BY-SA 4.0 via Wikimedia Commons.

Weight and Drag. The stabilator construction is simple compared to the stabilizer + elevator, having practically only a plate, and having no control linkages inside. This makes it lighter and produces lesser drag.
Stability. The stabilator design helps in eliminating the Mach tuck. Mach tuck is nose down tendency due to a change in the position of the centre of pressure. This is caused by a rearward movement of the shock wave which occurs in an aircraft in transonic flight. As the aircraft accelerates beyond its limiting Mach number or critical Mach number (the maximum Mach number it can operate), the elevator authority required to control the aircraft (to prevent a dive) increases beyond that of the elevator. The stabilator design prevents this.
Stealth. The stabilator design, with its clean lines and no discontinuities, offers more stealth compared to the stabilizer and elevator design. The design can also be optimised for stealth with edges etc.

Some GA aircraft do use all moving tail planes for e.g. Piper Cherokee. However, there are a couple of reasons this system is not usually used in civil aircraft:

Control Power. As already noted, the stabilator is hinged about the aerodynamic center, which means that the moment (and the pilot power) required is constant. In case of civil aircraft, the airplane must show an increasing resistance to an increasing pilot input. When they are used, the stabilators in GA aircraft have an anti-servo tab to provide more resistance.

Source: avstop.com

Requirements. There is no requirement in civil aircrafts for higher maneuverability or supersonic flight. In case of Concorde, the trim problem in transonic range was overcome by shifting fuel between the fuel tanks, thereby changing the center of gravity of the aircraft.


text:
Are high-frequency flapping wings efficient and scalable at high Reynolds numbers?
Is high-frequency flapping (similar to how dragonflies fly) an efficient lift production method at high Reynolds numbers?
I have not seen anyone develop wing suits with high frequency flapping, is it efficient only at the insect scale? A few million years ago there used to exist dragonflies with wing spans around 70cm - correlating with the high oxygen content in the atmosphere at that time - so is this possible at larger wingspans too?
I'm thinking of something like the parademons in Justice League:

Some English University researchers studied the tiny helicopter Black Hornet versus Colibri-wings as efficiency. It was shown that rotating wings have LESS LOSS as the flapping ones because the latter must surpass the inertia of the wings at each flap. The insect wings have little weight and so small inertia.  So high-frequency flapping is only for small devices. What is better in the animal wings is the aerodynamic itself> Search "leading-edge vortex" on Google. Why animals have no rotating wings? >there is no rotating device in animals, because they must be fully articulated, by design... Only maple-seeds have a sort of autogyro.

There are rotary devices in animals (if you count bacteria as animals): e.g. the rotary flagella motor of E. coli and other bacteria.

Relative to your included illustration, in addition to the inertial losses as cited by Adrian Marius, there's an issue of power-to-weight ratio related to building a flapping-wing flying suit.
Backpack helicopters (coaxial rotor type) are just about feasible, with short flight duration (a few minutes) and slow forward speed; thrust-hover systems likewise (turbofan jet belt from Vietnam era, twenty minutes at around 30 m/s and the more modern "Jet Pack" with larger ducted fans, somewhat better duration at similar speeds) -- anything less efficient at converting stored energy into lift or thrust will be either too low in reserve power or too short in flight duration for practicality, if not both.

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text:
Do ATC displays show the target altitude that the pilot has set in the autopilot?
When cleared to climb/descend to a level, the pilot enters that level in an altitude preset window, allowing the autopilot to climb/descend and level off at that level. Is this level, preset by the pilot, visible on an ATC radar screen?

Yes, our radar is indeed capable to display data of the Mode S Enhanced Surveillance Transponder like Selected altitude, IAS, Mach Number, Heading and more.
After issuing a climb/descend clearance and entering it into the sytem it would also warn us if the selected altitude is different from the cleared level.

Nice. Info from Eurocontrol, for further reading: http://www.eurocontrol.int/articles/mode-s-operational-overview - I hadn't heard of this, and I'm not sure the US is set up to use EHS. Is this just limited to some parts of EU?

I just can tell for Germany (where I am working) an Eurocontrol. I could imagine that Europe is, due to the high traffic demand, the only region where Mode S transponders are mandatory and therefore in the US this isn‘t set up

If the ATC Automation System supports the Display of Mode S - Enhanced Surveillance Data, Then ATC Radar will display the Level Selected by Flight Crew If the Aircraft is equipped with  MOde S - EHS Transponder.
The method of showing the Selected Level varies from Automation System to Automation System. The below image is an example for various data obtained from aircraft in an ATM Automation System.

The last two rows are the data down linked from the aircraft to the ATC Automation display. In case you are interested in knowing what are the other figures downlinked , its explained below in the same order as shown in the extended label picture.

ICAO Address;
Selected Altitude;
Heading;
IAS (Knots);
Mach;
TAS;
Ground Speed
Inertial Vertical Velocity;
Barometric Vertical Velocity;
Track Angle Rate;
Roll Angle;
True Track Angle.

ATC only sees the altitude reported by the Transponder, which is provided by a seperate Altitude Encoder.
In the US by Jan 1 2020, all air vehicles operating in most US airspace where radios are required are required to have ADS-B Out to report position & altitude over their transponder.
(Seems that airlines and the military will be late to the game, not having access to the same equipment that smaller planes are installing now or have already installed. Panel mount and remote mount units are being installed for certificated planes that fly IFR, and other non-permanently installed units for experimental & VFR only craft are also being connected.  Also, ADS-B In units for recieving other's position reports and displaying in iPad or similar are very popular.  My transponder has both and shows me traffic on my Moving Map GPS/Nav/Com unit.)

Thanks for the answer. Meanwhile, I did some more research myself, and I found out that the Mode S (Enhanced Suveillance) EHS contains the 'selected altitude' and, yes, is visible to the ATC radar.
(I fly in Europe and found the info on https://www.skybrary.aero/index.php/Mode_S#Functionality_2 and http://www.eurocontrol.int/articles/mode-s-operational-overview )

No. That information is contained within the automatic flight control system.  All altitude reporting to ATC comes from a radar transponder with an altitude reporting capability.

Given @pcfreakxx's answer, and Eurocontrol support for Mode S Enhanced, I'm not sure this answer is specific enough.

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Does anyone know an equation relating wingspan to gliding distance for a glider?
I found this equation online but it is not from a reputable source and has no derivation. Could anyone help me by deriving this equation or even verifying its accuracy? I would love to cite and use this equation in my assignment so urgent help would be most appreciated.

There is no such simple relationship. The wings profile shape also influences the Lift-to-drag ratio.

Merely the fact that the text and example discusses paper airplanes, wing spans the tens of cm range, and a launch height of 2 m, should hint that the formula probably isn't applicable to the general case, or even to all gliders.

Your mystery equation is
$$\text{Distance} = \text{Height}\cdot0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
Since the flight distance is the product of the glide ratio (or lift-to-drag ratio) L/D and height, the equation can be written like this:
$$\frac{L}{D} = \frac{c_L}{c_D} = 0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
if we use dimensionless coefficients instead of the dimensionful forces. Now that does look familiar, right? Only something seems to be missing. And that drag area $f$ should be the wing area.
Now you asked for the derivation, and I've done that only with wind in this answer, so let's do it for the simpler case of a glider and without wind right here. You start with the question: What polar point gives the best distance for a given height? Or, in other words, when does the lift-to-drag ratio reach its optimum? To get anywhere, you need a simple equation for the lift-to-drag ratio, so I recommend to start with the equation for the drag polar
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
The terms inside the big bracket are the sum of the parasitic and the induced drag coefficient and the term in front of the bracket is the product of dynamic pressure and wing area. It is needed to turn the coefficients into a force. The symbols are:
$\kern{5mm} \rho\:\:\:\:\:$ air density
$\kern{5mm} v\:\:\:\:\:$ velocity
$\kern{5mm} S\:\:\:\:\:$ wing surface area
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor, normally between 0.8 and 1.0
Since lift should be constant over speed for a glider, the optimum lift-to-drag ratio is when drag reaches a minimum. We express the lift coefficient by what it stands for and differentiate drag with respect to speed:
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\ c_{D0}+\frac{(m\cdot g)^2}{\frac{\rho\cdot v^2}{2}\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$
$$\Rightarrow\:\:\frac{dD}{dv} = \frac{2\cdot \rho\cdot v}{2}\cdot S\cdot c_{D0} - \frac{2}{v^3}\cdot\frac{2\cdot(m\cdot g)^2}{\rho\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$
Drag should reach its minimum when the derivative equals zero. We try to isolate the zero lift drag by dividing the equation by all what is collected around it:
$$0 = c_{D0} - \frac{2}{v^4}\cdot\frac{2\cdot(m\cdot g)^2}{\rho^2\cdot S^2\cdot\pi\cdot AR\cdot\epsilon}$$
Now bring $c_{D0}$ to the other side and re-insert the lift coefficient. The result is:
$$c_{D0} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
This means that the optimum lift-to-drag ratio is reached when the zero-lift drag equals induced drag. Total drag is the sum of both and in this case equal to twice the induced drag. Written in coefficients, this is:
$$c_D = \frac{2\cdot c_L^2}{\pi\cdot AR\cdot\epsilon}$$
Written as the lift-to-drag ratio, this becomes:
$$\left(\frac{L}{D}\right)_{opt} = \frac{\pi\cdot AR\cdot\epsilon}{2\cdot c_L}$$
Since the optimum lift coefficient can be expressed as
$$c_{L_{opt}} = \sqrt{c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
this can be inserted and the lift-to-drag ratio can be written as
$$\left(\frac{L}{D}\right)_{opt} = 0.5\cdot\sqrt{\frac{\pi\cdot AR\cdot\epsilon}{c_{D0}}}$$
The wing's aspect ratio is $AR = \frac{b^2}{S}$, and the mysterious drag surface must be $f = c_{D0}\cdot S$, and voilá, the strange equation is proven right. When the correct values are used, it is valid from mini paper airplanes up to Jumbo Jets and above. Airfoil drag is included in the zero-lift drag coefficient.

You may add links and references to provide further reading (I m curious about where this equarion cones from and who uses it for the first time)

Dear down voters, if you don't understand the answer, please consider asking in the comments instead of blindly down voting what is a correct answer.

@ManuH: Sheesh - are you guys never pleased? It’s the sum of parasitic and induced drag, plain and simple, and was most likely proposed first by Prandtl or one of his pupils.

it is not a question of being pleased but of having more references not only for further readings but also to ease navigation in external resources (I do believe it improve quality)

@ManuH: It is really the most simple and most often used of equations, so I was not expecting to defend its use. I added more explanation, but cannot really prove who has used it first.

You may be confusing wingspan with aspect ratio, roughly span over chord. More accurately, AR=square of wingspan divided by wing area. Still not the whole story on glide ratio, but it's most of it I think.
The FAA's Glider Handbook is a good starting reference.


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How can I verify if the quantity of fuel being used is correct?
Is there a formula to determine if the quantity of aviation fuel that is posted as being used is correct? If I have the number of gallons, the pounds and hours flown?

Welcome to aviation.SE! I don't completely understand your question. What is the "posted" value that you're talking about? Exactly what two things are you trying to compare?

Posted where?

The fuel for a typical GA aircraft is AvGas, 100LL (blue tint).
It weighs 6.01 lbs / gallon.
Gallons * 6.01 is the weight.  For example, if you're filling up a Cessna 172SP that holds 56 gallons, it should take 336.5 lbs. of fuel.
To calculate how much has consumed, you'll have to know the burn-rate of your airplane. Again, using a 172SP, the published burn rate is 13 g/hr, but most people lean to about 10 g/hr.  So you can expect that, per hour flown, the plane should use about 60 lbs. of fuel.
Of course, a plane will use more climbing, less descending, and a certain amount for ground operations.  So the exact details will depend on your flight profile.


text:
What are the minimum hours required for private instrument fixed-wing plus commercial helicopter?
I want to get my private pilot plus instrument rating in fixed-wing aircraft for personal use. In addition to that I want to get my private and commercial in helicopters to start a career in flying helicopters.
Does my flight time accumulated in both fixed wing and rotorcraft count towards my commercial rating? As in: 40 hours fixed private, then 40 hours fixed instrument. Then 30 hours helicopter private and 30 more hours for the commercial rating? That would come out to a total of 140 hours. All I would have to have would be 10 additional hours of flight time to qualify for my commercial.
I get that not everyone finishes in the minimum hours on everything, but that aside, am I reading the rules correctly? Or would it be 150 hours in helicopters only?

The 150 hours is flight time which is not category or class specific so hours in both airplanes and helicopters would count towards the 150 hours.  You are missing an instrument helicopter rating.  It is in addition to the instrument airplane rating.
Below I try to sum up the minimum hours required for each certificate and rating if obtained under Part 61.  Part 141 schools require different hours.  You actual experience will vary considerably.  I would first get a private pilot airplane and helicopter certificate and then work on the instrument ratings concurrently.  Afterwards, work towards the commercial helicopter rating.

To get a private ASEL certificate:  You need a total of 40 hours
flying time to that meets 61.109 experience.
To get an private helicopter certificate addon:  An additional 30
hours of training is required.  You will already have more than 40
hours total time.  Total time at this point would be 70 hours minimum plus the flight time for the practical tests.
To get an instrument rating for both airplane and helicopter: You will need 50 hours of PIC cross country time plus 40 hours of simulated or instrument time.  The 3 hrs simulated time required by the PP ASEL should count towards that 40 hours.  You must have at least 15 hours each with a CFII in both airplane and helicopter (total 30) and if they are all cross country flights that will help your cause.  You already started with a minimum of 8 XC PIC hours from your private certificates.  The remaining 12 hours along with 7 hours of simulated time can be accumulated in either airplane or helicopter.  Total time up to this point should be 120 hours plus the flight time for the instrument rating practical tests.
To get a commercial helicopter certificate:  A total of 150 hours total time (all the above counts) and 50 hours of helicopter time.  (You should already have 45).  35 hours of PIC helicopter time (Already have 20) to include 20 hours of training on commercial maneuvers, 10 hours solo and 10 hours of helicopter cross country time.  The way I see it, is the commercial will add an additional 30 hours to your total time giving you exactly 150 hours.

+1, but one minor point: an instrument rating isn't required for commercial so it isn't necessarily "missing". You might also want to mention that your answer assumes part 61; part 141 usually requires fewer flight hours but a lot more ground school time.

I agree with you on the instrument rating.  As far as hours go, it is a free rating as it won't add anytime to the totals if done in this manner.  Besides, who wants to have a limitation on their commercial certificate.  I will update for 61 schools.  Thanks


text:
Does in-flight Wi-Fi require regulatory approval?
Does any country have regulations that require a certificate or approval of the aircraft that use portable Wi-Fi in flight? Is there an FAA or EASA regulation or advisory, or an ICAO document or advisory?

fyi, Wi-Fi does not stand for "Wireless Fidelity" see this question

I've edited your question to try to make it clearer, I hope I didn't change it too much. But what does "use portable Wi-Fi in flight" mean? Are you asking if the aircraft's passenger Wi-Fi system requires approval, or if the crew needs approval to use it, or something else?

Thank you very much for this correction sir.  “use portable wi-fi in flight”. I mean. Some of the aircraft in some airline provide wifi for used by passenger for communication or browsing. I am looking for faa, icao or any state regulation. How to certified or approve this aircraft that provide wifi for passenger.

The FAA touches upon it in this letter

Current FAA regulations require an aircraft operator to determine that
  radio frequency interference from PEDs is not a flight safety risk
  before the operator authorizes them for use during certain phases of
  flight. Even PEDs that do not intentionally transmit signals can emit
  unintentional radio energy. This energy may affect aircraft safety
  because the signals can occur at the same frequencies used by the
  plane’s highly sensitive communications, navigation, flight control
  and electronic equipment. An airline must show it can prevent
  potential interference that could pose a safety hazard. The PED ARC
  report helps the FAA to guide airlines through determining that they
  can safely allow widespread use of PEDs.

The operator is responsible for determining that the unit does not create any interference they link off to this document which is pretty verbose and outlines a lot of the info you may be looking for on this front.
This document elaborates a bit more on the regulations

Aircraft with an FAA-approved system— such as an Onboard Mobile
  Telecommunications System (OMTS), Wireless Fidelity (WiFi), airborne
  access systems (AASs), or Network Control Units (NCUs)—are considered
  PED-tolerant for PEDs used with the installed system. If an aircraft
  model has demonstrated tolerance for both transmitting and
  non-transmitting PEDs, the operator may allow PED use during all
  phases of flight on this aircraft model.

Aircraft need to be shown to be PED tolerant for Wifi units. You can find an AC covering whats involved in that here.


text:
How does angle of incidence affect an aircraft's stability?
How does angle of incidence affect an aircraft's stability?
I've tried searching the web for the simplest answer that makes sense but so far I've come up with nothing as yet.
I know it sounds simple, but I'm still new to this so its pretty hard to grasp my mind around the concept yet.

It does not sound simple, it sounds like a strange thing to ask, which is probably why you couldn't find much on it. Because angle of incidence (of the main wing) is determined by other criteria and then other parameters (wing longitudinal position and horizontal stabilizer) are adjusted to achieve longitudinal stability. What makes you ask it?

@Jan Hudec I only need to know how the changes in the angle of incidence affects an aircraft's stability.

The angle of incidence is the angle between the wing chord and longitudinal axis of the aircraft as depicted here. From years of building model aircraft and flying aircraft I can explain one way that it affects the aircraft, and that is by reducing drag caused by the fuselage. A given wing requires a certain angle of attack (pitch up attitude) in order to fly at a given weight and speed. If the angle of incidence is 0 degrees, then that would require a nose high attitude and expose more of the underside of the fuselage to the relative wind. However, having an appropriate angle of incidence allows the fuselage to have a more horizontal orientation (and better visibility for the pilot from the cockpit) than if the wing was mounted exactly parallel to the longitudinal axis of the fuselage.
So how does it affect an aircraft's stability? It affects an aircraft's stability by reducing its drag at certain airspeeds.

Uh? We have longitudinal, lateral and vertical stability. Which one are you saying increased incidence is a positive effect?

@jwzumwalt you are very observant. This answer doesn't really address whether longitudinal, lateral and vertical stability is increased or decreased.  I was only able to explain what I know about the effects of the angle of incidence. Perhaps someone else will provider a more detail analysis. :)

Thanks for the kudos... what I would expect in your answer is the possibility of a change in center of lift. This would change the pitch stability (about the longitudinal axis), though I don't remember which direction - go for it! ( I suggest a diagram) FYI, increased drag behind the cg would increase stability in all three. but as I remember it center of lift is in front of CG and therefore an increase in incidence would be a destabilizing effect. :)

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text:
Do I need a physical print-out of weight & balance calculations onboard
Our flight school taught us to print out some documents relevant to flight preparation and take them onboard the aircraft: This usually included
weight & balance as well as takeoff/landing performance at dep./dest. airports.
I believe this was established as best practice, but not mandated by SERA.
Am I required to have paper versions of certain documents onboard the aircraft at all times?

Weight & Balance:

SERA Annex VII (Part-NCO)
Non-commercial operations with other than complex-motor-powered aircraft
Subpart C: AIRCRAFT PERFORMANCE AND OPERATING LIMITATIONS
NCO.POL.100 Operating limitations – all aircraft

During any phase of operation, the loading, the mass and, the centre of gravity (CG) position of the aircraft shall comply with any limitation specified in the AFM or equivalent document.

and
SERA Annex VII (Part-NCO)
Non-commercial operations with other than complex-motor-powered aircraft
Subpart A: GENERAL REQUIREMENTS
NCO.GEN.135 Documents, manuals and information to be carried

The following documents, manuals and information shall be carried
on each flight as originals or copies unless otherwise specified:
(1) the AFM, or equivalent document(s);
(2) the original certificate of registration;
(3) the original certificate of airworthiness (CofA);
(4) the noise certificate, if applicable;
(5) the list of specific approvals, if applicable;
(6) the aircraft radio licence, if applicable;
(7) the third party liability insurance certificate(s);
(8) the journey log, or equivalent, for the aircraft;
(9) details of the filed ATS flight plan, if applicable;
(10) current and suitable aeronautical charts for the route area of
the proposed flight and all routes along which it is reasonable to
expect that the flight may be diverted;
(11) procedures and visual signals information for use by intercepting
and intercepted aircraft;
(12) the MEL or CDL, if applicable; and
(13) any other documentation that may be pertinent to the flight or is
required by the States concerned with the flight.

So, per SERA, the weight & balance sheet does not need to be carried on-board. Pre-flight weight & balance calculations must show that the airplane remains within loading limits from takeoff weight to landing weight.

Paper & Digital Versions:

Edit:
GM1 NCO.GEN.135 Documents, manuals and information to be carried now reads:

The documents, manuals and information may be available in a form other than on printed paper. An electronic storage medium is acceptable if accessibility, usability and reliability can be assured.


text:
Approved Mixtures of Fuels in ROTAX 912 Engine
The Rotax 912 is a popular combustion engine in smaller general aviation aircraft in Europe. Due to a number of factors (including fuel cost), the Rotax-powered aircraft in our flight school are most often run on MOGAS (Super 95). Since smaller airfields don't always have MOGAS available, they are frequently flown on mixtures of AVGAS and MOGAS during longer flights.
Going through the technical documents of the engine, I never found a passage mentioning explicitly that these different fuels can actually be mixed. I was wondering why that is, considering the great length to which the manuals go to cover all potential combinations of operating fluids (lubricants, coolants, fuels).
The authoritative reference for the approved fuels of this engine is the Service Instruction Document Rotax SI-912-016R14 (linked here is a slightly outdated revision).
It does mention:

The following fuels can be used.

and goes on to list MOGAS and AVGAS of different octane ratings. The only passage where mixing of fuels is mentioned explicitly cautions against a potentially low octane rating of the mixture:

Any mixture of unapproved fuels and/or additives that cause lower than the specified octane rating can cause engine damage like e.g. detonation.

Not having a background in combustion engines, I can only speculate that perhaps it is implicitly clear that any mixture of approved fuels would also be safe for the operation of an engine?

this isn't an authoritative answer, but the Vans crowd has found that mixing some 100LL into mogas (91-95 octane) helps reduce vapor lock.

Right in the document you linked:

Fuel For ROTAX® aircraft engines different fuel types are
available. See Operators Manual of the relevant engine type

This means the specific manual for a specific engine and airplane (serial number specific) and its various supplements and added certificates.

Suitability of fuel system components of airframe ROTAX® urges owners
to confirm with there airframe manufacturer that ethanol blended fuels
of up to 10% (E10) are compatible with all fuel system components. It
is the responsibility of the aircraft manufacturer to test their fuel
system components and supply any further information on techniques,
procedures and limitations of using ethanol blended fuel. ROTAX®
recommends that aircraft manufacturer and owner/operators read the
following:

FAA Advisory Circular Letter AC 23.1521-2
FAA Special Airworthiness Information Bulletin CE-07-06
EASA Safety Information Bulletin – SIB 2009-02 These contain details regarding the use of ethanol (alcohol) blended fuels and the type
certificate requirements. It is strongly recommended that also
non-certified aircraft also conform to the information given in the
above documents.

This is the closest you will get to authoritative generic information related to what you are asking. The real issue is that unlike avgas, Mogas is not a consistent formulation and the engine and aircraft manufacturers cannot possibly test all mixtures of all brands for compatibility with avgas.
Not all MoGas is the same, there is traditional formulation (similar to avgas but wider tolerances and occasionally still sold for racecars) and several "reformulated" highway gasolines including various gasohols and "non-ethanol".
In the USA I have never seen an aircraft that allows gasohol, even those specifically rated for highway gasoline still call for "Non-ethanol" formulas, which use an ether compound as the oxygenator rather than alcohol. The engine may be rated to run on e10 but that does not mean the whole system is rated for e10.
Reasons include storage stability, moisture and temperature issues, corrosion, seal compatibility, and the predictability of the antiknock rating of mixed fuels. Vapor pressure curves also contribute.
(Avgas has anti-oxidants and the longest storage life by far at several years in a good container. Gasohol like e10 goes bad in a couple of months, non-ethanol may be good for 6 months to a year.)

Excellent point being made that the whole system is to be taken into consideration when deciding which fuel (mixtures) can be used. Knock resistance of the fuel as such is not the only concern.


text:
Is it viable to put an engine at the rear of the plane like in this photo?
I saw this image on a NASA page talking about hybrids and I was wondering if the back-engine placemente is actually viable and if it is why hasn't been done yet?

"why hasn't been done yet?" one word: tailstrikes

Doesn't any single-engine jet effectively have a back engine - or at least back exhaust - placement, given obvious weight & balance limitations?  Not to mention a number of pusher prop planes.

This configuration (STARC-ABL) is also aimed to reduce drag and energy consumption by absorbing the turbulent fuselage boundary layer in the continuation of Boeing SUGAR program.

Until somebody loads the plane improperly and tips the tail.

As you look closely to the picture, there are also engines located under the main wings. Thus this is a trijet, a concept that has been used in the past by for example the MD-11, Lockheed tristart and Boeing 727. The main reason for choosing a trijet configuration was the ETOPS requiring twin engine aircraft to always be within a certain range of an airport. This was in a time when engines where less reliable. With three engines the aircraft did not have to bother with ETOPS regulations allowing it to fly routes impossible to fly for twin engine aircraft. But as engines became more reliable and the ETOPS got lengthened the trijets became redundant.
A big downside of the trijet is the structural complexity of an engine in the back, the fuselage needs to be reinforced to withstand the extra forces. From a maintenance perspective it is difficult to access the middle engine because it is high of the ground requiring a stair for visual inspection. Then there is the economical aspect, if you can do it with less engines it will always be more fuel economical. The next iteration of 777 can carry as many passengers as the 747 with half the engines.

I don't think this is right ... what's unheard of on this design is not the rear choice for the engine, but more the fact that the rear engine is centered on the fuselage while a tri jet such as the MD11 have it offset (up)

You completely missed the reason the aft engine is here. It's not for escaping ETOPS, but to suck air flowing along the fuselage instead of the free air stream in the hope this will reduce aircraft total drag. Conventional trijets exist, this is not one of them.

The question mentions only "the placement" of the back engine, not the shape of the intake.

@mins, I'm aware that the reason NASA put the engine here is for the boundary layer ingestion, but the question asked here was more general about placement of the engine in general indicating that the asker is not aware of the trijet concept.

@Antzi: Most trijets have the rear engine centered on the fuselage; the DC-10 and MD-11 are the exception in that regard.


text:
Have there been attempts to break Jean Boulet's 1972 helicopter records? (highest altitude and longest unpowered descent)

So this is the incredible photo of a man accidentally setting a world record.
In 1972 a French pilot named Jean Boulet set out to break the world record for the highest altitude ever reached in a helicopter. It was an extremely dangerous stunt that easily could have cost (him) his life. But since Jean was a very talented pilot and he felt that he could do it.
Despite the rapidly thinning air, Jean just kept pushing forward. It wasn't until he had reached an insane height of 40,820 ft and his helicopter just physically couldn't go any higher that Jean finally began to descend back towards the ground.
But although he had managed to break the world record, he wasn't safe just yet. As Jean was descending, his helicopter's engine suddenly died. Since he had removed his battery and starter to make the aircraft lighter, he had no choice but to try an emergency maneuver called auto rotation to collide himself towards the ground. Autorotation by itself is already extremely difficult, but for Jean it was nearly impossible since he couldn't see anything due to the clouds, and he also didn't have any altitude instruments onboard.
Despite everything however, incredibly he actually managed to make a safe landing accidentally setting a second record for the highest unpowered helicopter landing. And to this very day both of Jean's records remain unbroken.

This is the extracted transcript from Andy Jiang's YouTube video He Accidentally Set This World Record but seems to check out with Wikipedia's Jean Boulet; Aviation records
Question: Have there been attempts to break Jean Boulet's 1972 helicopter records? (highest altitude and longest unpowered descent)

Appropriate username for the question. I reckon that's exactly what he said when the engine died.

Although there are not many publicized records of people attempting to beat this record, a man by the name of Fred North supposedly took a AS 350 B2 "Squirrel" 12954 meters high. This would technically would mean he beat Jean Boulet's record. However, Since the FAI (Federation Aeronatique Internationale) does not recognize this record it is likely that Fred North either broke a rule or lied or did something else that made them not recognize the record. I would reference the FAI page but it wouldn't load for whatever reason.

Thank you for pointing that out I will make sure to cite websites moving on

On PPRUNE it is mentioned:
"... he fails to tell us how, with all his elaborate planning, he could forget to inform the FAI of his attempt, and how he could forget to bring along a sealed barograph. He also forgot to tell us how he knows he was at that high altitude. He told us in breathless prose everything else that he did that day, so I am left with the unfortunate belief that this was a publicity stunt, and not a legitimate altitude record. If he is available, perhaps he could help us understand the omissions."


text:
Why do aircraft (namely military) need/use formation lights?
Why are formation lights used,and why are they largely/always used only on military aircraft and not civilian?

Formation lights are used so that aircraft can fly close formation at night.  They are typically luminescent strips positioned so that an aircraft can be in the desired position (i.e. fingertip formation) and have references fore-aft, up-down, and near-far similar to references as used for daytime formation flying.  Something along the lines of, "keep the position light just below the formation light (strip) under the cockpit and the aft fuselage light (strip) just touching the wing hardpoint, and you're in the right position.  If the position light goes farther below the strip, you're getting high; if the hardpoint is sliding back into the aft light you're getting close, etc."
Obviously these references are very specific to each individual aircraft.
You can see the formation lights in this picture of an F-14; the dots are actual position lights, while the strips are the formation lights.  Source

As to why only military aircraft have them... how often have you seen or heard of civil aircraft flying formation at night?  Yeah, me neither.  There are very, very few non-military reasons for formation flight, and essentially none that require it to be done at night.

Stupid question but do they not help the enemy spot you?

@curious_cat: I think a lot of it is just down to the sort of military mindset that just loves regimentation.  Basically the same reason I spent seemingly endless hours doing close-order drill in boot camp, rather than practicing something that might have been of practical use in the jungle.

@curious_cat it is more about "pucker factor" than "regimentation". In a combat zone where there is a plausible surface-to-air threat, form lights are turned down or completely off. This slightly increases the likelihood of mid-air bumps/collisions, but greatly decreases the likelihood of being seen by an unaided ground threat. Aided-vision (NVGs) may still see the aircraft, but it is much harder and still difficult to integrate with surface-to-air targeting systems.

From the practical standpoint I can remember vividly two times where the formation lights were invaluable. First, let me say I always used them while flying formation in clouds. They just gave you a little more light to fly off of. I flew A-7Es - light attack single seat fighter jets - off the USS Nimitz for two tours and was stationed in the soup of the Mediterranean.
With respect to flying in clouds, I was with my lead as we were coming into NAS Cecil Field in the summer. It was a nice day and we were with approach control being vectored to the VFR initial at the speed. At some point we were approaching a cumulus cloud and I tightened up my position on the lead. Entering the cloud he nearly disappeared from me. The cloud was the densest cloud I had ever encountered. I was tucked in uncomfortably tightly and asked him to turn on his formation lights, which allowed me to see him better. Very useful that day.
The second time was with a training flight we did off the carrier. I was always looking for cunning ways to "train like you fight, and fight like you train." We often did intercept runs with the F-14s at the end of our hops. We would be vectored on separate channels by the E-2 to positions 20 nm apart with 1,000 ft of altitude separation, or something like that. We would come toward the F-14s at constant altitude and constant heading. The E-2 and the F-14s would practice vectoring in on targets, hand off, and target acquisition. We would pass by one another, head out, turn around and do it until we ran out of time, or they ran out of gas.
The other JO was the lead and it would be a beautiful night out there. Clear skies and a full moon. I asked Turk if he wanted to have some fun. "Sure, what do you have in mind?" I briefed the flight. Turk got airborne first and as is customary gave his departure call that he was airborne. This was so the E-2 could keep track of who got airborne and who didn't. He went out to our rendezvous location and waited. When I got airborne I never made my departure call, and just headed out to join my lead. We went off and did our bombing on flares dropped on the ocean. After finishing that part of our mission we headed over to play targets for the F-14s.
Inbound, before checking in with the E-2, Turk turned off his anti-collision lights and had his formation lights on so I could nestle in close to his wing. This was okay because the E-2 had Turk's aircraft and kept separation for both us. We checked in and the E-2 set us up for intercepts.
On the beginning of first run, I was tightly tucked in on Turk, and the E-2 gave the F-14 flight our contact information, "I have one target at twelve o'clock, 20,000 ft." The F-14 lead confirmed the information, and then asked about the second aircraft that was supposed to be in the flight. The E-2 told them that they had no record of the aircraft getting airborne. They weren't buying it, and we listened on their radio frequency as they tried to piece together the fight as they were rapidly closing. "Where's the second target?" At one point there was a call, "Got 'em!" He is at five miles abreast and 4,000 feet low." We had them.
Their search radars were capable of discriminating one target where there were two. Visual can be obtained at around eight miles and so when their vector was "12 o'clock at 8 miles," the lead turned on his anti-collision lights and I broke away doing the same, forming a pincer attack on the two unsuspecting fighters. When they saw two contacts where there had previously been one, the trap was sprung. There were hurried calls of two targets separating, and...
I ended up on the six of one of the two F-14s and he was nose low in a descending right hard turn. When he hit burner I called a Fox two, and looked over my shoulder high to the left and saw my lead chasing his F-14 nose high in a tight left turn. When he went in to burner it was a beautiful sight, a long tail of flame from both exhausts and Turk called his shot. We were still turning. With experience, combined with graciousness, the other lead called, "Knock it off, knock it off," the standard call to end an ACM engagement.
It dawned on me that we had never checked the flight schedule to see who would be the pilots in that flight. Was it the CO or XO? We were either lucky, or the F-14 crews liked the training opportunity. That lesson will never be forgotten: "I don't want to be tricked like that again." Never heard back from the crew when we got back to the ship. You have to understand, we fought F-14s pretty regularly and at best could hold them to a neutral fight. This was a nice friendly get back.

I read that story when you originally posted, but just realized, you never indicated what you were flying. Thanks for the great story, and thank you for serving!


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Are the Airport Operational Databases at major airports in the US available to the public?
Are the Airport Operational Databases at major airports in the US available to the public? I am pretty sure it is not live but maybe released a month or so after.
AODB
An AODB system is usually the core IT system to support the airport ground operations, it integrates with various systems from the heterogeneous IT landscape found at the airport, compiling data from airlines flights schedules, flight plan management, communication between airlines and airports to building management systems, live ground movements and many more systems.
It serves as platform for CDM (Collaborative Decision Making) for the various parties forming the airport community, from airport operators, airlines, groundhandling agents to ATC.
It handles seasonal and operational flights by providing both real-time and historical data, supports resource management for facilities and equipment, as well for staff, it is an information portal.

I've never heard of an airport making that much raw data publicly available. Many airports are run by public agencies, so you could try making a public records request for specific reports or documents under whatever local freedom of information law applies (if any), but that wouldn't be the same as the entire airport database. Some airports do make their flight information display system FIDS publicly available online, showing roughly the same information as the displays in the terminals.

thanks, i figured they wouldn't release that much information


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How to calculate the induced drag coefficient?
In an exercice of Flight mechanic, I have to compute the drag coefficient at zero lift: $C_{D0}$.We saw in class two ways to find it :
$$
C_{D0} = \frac{\pi AR e}{4E_{max}^2}
$$
With $AR$ the aspect ratio, $e$ the Oswald number and $E_{max}$ the maximal Lift-to-drag ratio. I don't have the value for the two last ones in my exercice so I can't use this formula.
We saw another way, by using the polar definiton: $C_D = C_{D0} + kC_L^2$ with $C_D$ the drag coefficient, $C_L$ the lift coefficient and $k$ the induced drag coefficient. In order to use it I just need to find the value of $k$ but the only formula that I have is:
$$
k = \frac{1}{\pi e AR}
$$
And I still need the value of $e$ the Oswald number. Is there a way to compute $e$ ? I didn't found any on Internet. If not, is there another way to compute $k$ without $e$ ?
Thanks for your help and sorry if I don't have the proper english vocabulary.

Is it only a wing or you have other surfaces or fuselage? If it is only a wing, then there are estimates for the Oswald factor and you don't need CFD. Of-course, these are estimates, but people designed airplanes before CFD also...

Even in the presence of other lifting surfaces and fuselages you can still find estimates. There are formulas for interference drag in classical aerodynamics texts.

There's no way to calculate $e$ without using computational fluid dynamics (CFD) since it involves the calculation of complex three-dimensional flow interactions with the wing geometry (lift loss due to wingtip vortices).
For most aircraft, 0.8 is a pretty good estimate, so this is probably the value you're expected to use. If you need a more accurate number for your particular problem, you'll either have to know the specific aircraft model (in which case you would likely have to calculate $e$ given $AR$ and ${C_D}_0$, $C_D$, and $C_L$ for a certain state) or be given a number to use for the problem.

Thanks! In class we studied an airplane close to the one in the exercice, and $e$ was equal to $0.85$ so I'll take this value.

In the course of looking for other aero data I stumbled across this rather old question.  For any future searcher like myself I thought to add a bit more info in case it could be useful.

e - Oswald efficiency factor is a way to categorize any deviation from the ideal elliptical lift distribution.
Idealized lift can be achieved in an untwisted wing by having an elliptical chord distribution (think about the Spitfire planform)

You can often infer by visual inspection the shape of the wing and other characteristics possibly twist, dihedral, taper etc and make an educated guess. Anywhere in the 0.75-0.95 range is probably safe.
For a technical reference on how to calculate this refer to Estimating the Oswald Factor From Basic Aircraft Geometrical Parameters


text:
Dynamic modes at supersonic speed
Our teacher gave us an assignment where we have to study the longitudinal stability of an X-15. I have to study it at 353.9 m/s which is Mach 1.2. Another group has to study it at 235.9 m/s so Mach 0.8.
I made a Matlab code computing the eigenvalues of the A matrix because I have to plot the phugoid and the short period modes. With my speed I get :
Eigenvalues [at 353.9 m/s]:
  -0.6094 + 3.1782i
  -0.6094 - 3.1782i
  -0.0775 + 0.0000i
   0.0473 + 0.0000i

While with the other speed I get:
Eigenvalues [at 235.9 m/s]:
  -0.4093 + 2.1175i
  -0.4093 - 2.1175i
  -0.0070 + 0.0649i
  -0.0070 - 0.0649i

In the second case, it is clear that the phugoid is the -0.0070  ± 0.0649i and the short mode is  -0.4093 ± 2.1175i. While in the first case, what can I deduce ?
Is there a dynamic mode which is cancelled by the supersonic speed?
EDIT: The A matrix is the coefficients of the longitudinal motion equations:

At 353.9 m/s:
 your phugoid mode is unstable as well as degenerated (Poles lie on real axis and has damping ratio 1).
while at 235.9 m/s:
phugoid mode has become stable as well as oscillatory and has some damping and frequency.
so, nothing has been canceled its just phugoid mode poles changing positions.
you can check it clearly by plotting root locus using rlocus command on MATLAB.

Thanks, it really helps! So what does my values -0.0775 and 0.0473 represents? I know that they are the roots on the root locus (one is stable, -0.0775 and one is unstable 0.0473) but physically, for the short period I have only one frequency while here my phugoid mode will have 2 frequencies?

@Louis The phugoid has split into two real-valued eigenvalues. They are no longer "frequencies".

@Louis The phugoid mode is now a first order mode which has time constant not frequencies


text:
When can I log PIC time in a new category of aircraft?
I am currently a Private Pilot Rotorcraft and I am doing an addon for ASEL. When can I log PIC time?
I've been told it's only when you're the solo occupant but after some reading I'm not so sure. 14 CFR 61.63(d.2) says:

Have received training required by this part that is appropriate to
  the pilot certification level, aircraft category, class, and type
  rating (if a class or type rating is required) for the aircraft to be
  flown, and have received an endorsement for solo flight in that
  aircraft from an authorized instructor.

Do you have to have your license in category to log pic time? Or is it after you have received your instructor's endorsement to fly solo per 61.63?
When I showed this to my instructor and we did the endorsement in my logbook we received some backlash from the flight school saying that PIC time is only accrued after you have your PPL in the applicable category of aircraft. During my flight lessons I was always operating the aircraft for the entire duration of the flight after I had received my solo endorsement which satisfies the requirements for PIC time per 61.51(e.IV).
Am I misinterpreting the rules? Can someone point out to me why I wouldn't be able to log PIC time even though it's in a different Category? Thanks for the input!

Related

Short answer: you can log ASEL PIC time only while flying solo, not while flying with an instructor.
You seem to be mixing up a few regulations: you quoted 61.63 but the text is actually from 61.31. However, since neither of those regulations are about logging time anyway, they aren't directly relevant.
The rules on logging PIC time are in 61.51:

(e) Logging pilot-in-command flight time. (1) A sport, recreational,
  private, commercial, or airline transport pilot may log pilot in
  command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an
  aircraft for which the pilot is rated, or has sport pilot privileges
  for that category and class of aircraft, if the aircraft class rating
  is appropriate;
(ii) When the pilot is the sole occupant in the aircraft;
[...]

(e)(i) says that you can log PIC time as sole manipulator only if you're rated in the aircraft. In your case, you aren't rated for ASEL (yet!) so you can't log ASEL PIC time while flying with an instructor, even if only you touch the controls. This is probably what the school is referring to.
However, (e)(ii) says that a private pilot who is the only person on board the aircraft may log PIC time, without any additional requirements (although other regulations do require an endorsement in order to solo, as you said).
That means, you can log solo ASEL time as PIC, but not training time with an instructor.

It would be the same as when you could log PIC time in rotorcraft, that is when you are the solo occupant or after you are rated (passed the check ride) in category and class. Once you get the add on ASEL certificate, any time you manipulate the controls you log PIC, even when getting DUAL.


text:
Why do Russian jets make a squealing sound?
Why do the engines noise from the Russian and Soviet jet create a squealing sound which is very distinct which most of the western jets don't have? Which part of the engine creates the noise, and why is it so distinct to Russian engines? Also it appears to be dominant in low rpm or at idle throttle setting.
You can hear this in the video MiG-29 start-up to shut down (4 min mark) .

I am by no means an aficionado of Russian fighter aircraft, but I suspect the sound you speak of is caused by intake airflow.
Since Soviet times, their aircraft have ascribed to a design doctrine of being able to fly from damaged or sub-standard airfield surfaces, and incorporate undercarriage & engine intake designs that assume constant presence of engine-killing FOD. They have either a meshed grating, or even an impervious retractable door flap that completely covers the intakes, while having additional doors open on top of the engine intake area to compensate, for ground operations.
At the 3.10 mark in the video, you hear what is probably the No1 engine spooling up, at about 3.35 you hear the No2 (closest to camera) starting to spool up - within a few seconds you will see a series of small doors above the red number "70" open. This is where the engines are drawing their intake air, away from ingestion of gravel, discarded hardware, small animals & the closely-milling, unconcerned ground crew.
I suspect that the restriction/turbulence caused by this slightly torturous air path is causing that high-pitched sound. It could also possibly be compressor bleed air being dumped as a normal part of low engine revs/idling.
At the 9.00 point in the video, you can see the flight intakes completely shut, with the ground intakes open, as it taxies in. Eventually, you even see a ground crewman appear to actually stand in front of the flight intakes while at least one engine is still running.
There is some discussion & a photo on this page
Would it be viable to install a screen in front of jet intakes to prevent them from sucking in birds?
This aspect of airframe design is a common subject of comparisons between US & Soviet/Russian design doctrine.

Whoa, that's some rugged design philosophy used by the russians. Thanks !

The main reason is because the air bases themselves were poorly maintained by western military standards and FOD was a fact of life.

It's difficult to pave runways in remote places in Siberia due to logistic problems and because tarmac won't last long in the harsh weather and the ground is too soft for concrete. Since defence of the Russian far East required airbases in such places, being able to operate from unpaved (gravel) strips was a design requirement for most Soviet military aircraft. (Canada has such places too, but it can be more easily defended from more accessible places).


text:
Why would a turboprop be better than an internal combustion engine for a UAV?
Let us consider a UAV, long endurance high altitude (~26,000ft). Why would a user (most probably military) go for a turboprop rather than an internal combustion engine?

What does IC mean?  Internal combustion, meaning piston reciprocating?  Because a turboprop is internal combustion...

Harish, aviation gas turbine engines (aka open cycle engines) are IC engines too.

IC meaning, traditional internal combustion engine. Those working on otto or diesel cycle.

I would call those "piston" or "reciprocating" engines.

@HarishRajan, Internal combustion engine means engine where the combustion occurs inside the working fluid. It can be piston, turbine or a combination (turbocharged piston engine). This is in contrast to external combustion engine where the working fluid, usually steam, is heated in a heat exchanger (boiler). Steam engines can also be either piston or turbine, the later being common in power generation.

Mostly reliability, and weight.  A TP is far more reliable than a piston engine, and much lighter.  The TP's lighter installed weight makes up some for its higher specific fuel consumption.
You would use a piston engine to get operating costs as low as possible, and you're willing to live with lower reliability (you're forced to use turbocharging or supercharging, which reduces reliability further), and one of the new turbo-diesels would be the best option in that case (close to half the fuel burn of a TP and able to run on kerosene, or diesel perhaps).

The maintenance counts in operating costs too and a piston engine requires a lot more of it.

Thank you, for the answers

Reciprocating engines are somewhat more efficient, but they don't scale up well. A larger piston engine can't have as large RPM, but that means weight grows much faster than power. That's not a problem for ships, where huge diesel engines are common, but it is a big problem for aircraft.
On the other hand, turbines are very light for power even when large, and the larger ones are even more efficient.
That's why nobody even makes aircraft piston engines with more than about 170 kW. The higher power range is served exclusively with turbines. The common ones start around 400 kW and go well into megawatt range (largest turboprop, Kuznetsov NK-12, produces 11 MW and the turboshaft variants derived from large turbofans go up to the 40–50 MW range).
Additionally, turbines are significantly more reliable and require less maintenance. In piston engines, the pistons, but also valves are subject to huge linear accelerations, which causes a lot of vibrations and wear, plus there are many additional rotating components linking it all together. In addition to at least one turbine-compressor pair, because a piston engine to operate up at 26,000 ft will have to be turbocharged, otherwise the thrust-to-weight ratio would be way too low.
In contrast a turbine had just a turbine-compressor pair and a turbine driving the propeller, everything just smoothly rotating even though at huge angular speeds (in the PT6 the core goes up to about 45,000 rpm and the power turbine to about 30,000 rpm) with much less wear and vibrations. That means fewer inspections and overhauls, and fewer parts to stock and replace and that saves a lot of money.

Because of the air pressure at 26000ft the IC engine would have very little power without forced induction (turbocharger/supercharger) you then need boost control at lower altitudes to stop the engine exploding from cylinder pressure. You can't use a carburettor because you would get carb icing too, so it necessitates fuel injection. All these things make control far more complex.
The other thing is the vibration of a piston engine, this could affect camera focus or other unknown instruments.

You actually can use carburetors at higher altitudes.  Here's a carb for a Wright R-1820: https://airandspace.si.edu/collection-objects/wright-cyclone-r-1820-engine-carburetor/nasm_A19640058000  That engine was used in many WWII aircraft, like the B-17, that flew at altitudes above 30,000 ft.

Fleet-wide fuel and parts standardization, and use of an approved and well-known powerplant; and the UAV is likely derived from a piloted vehicle which had been built around the turboprop.


text:
Does the Cessna 152 or 172 have emergency door cable releases?
Is there such a thing as an emergency cable release inside the cockpit of 152 or 172, to remove the door hinge pins in an emergency?

The Cessna 150 Aerobat and 152 Aerobat both have jettisonable doors.
I don’t believe any version of the Cessna 172 does as there in no aerobatic C172 versions.
This Photo shows two “D” rings which are pulled to jettison the doors.

That's a nice blue sky you've got there, be a shame if something were to happen to it...


text:
What is the meaning of "pass well clear" in the ICAO right of way rules?
ICAO Annex 2 states under 3.2.2.1:

An aircraft that is obliged by the following rules to keep out of the
  way of another shall avoid passing over, under or in front of the
  other, unless it passes well clear and takes into account the effect
  of aircraft wake turbulence.

How should the term "well clear" be correctly interpreted?
Does this sentence also imply, that the right of way rules only have to be applied, if the expected minimum distance to the other aircraft is below "well clear"?

This is probably one of those rules which is deliberately a bit open to interpretation. For example, a glider pilot will be happy to pass under another glider when hill soaring at 40 knots much, much closer than they would be if cruising at 100 knots! Other pilots will probably use standard separation minima, for example 500 feet might be acceptable in the powered circuit but 1000 feet is allowed in certain airways.
SKYbrary suggests that "well clear" means 500 feet, but again points out that it might not be sufficient when using TCAS.
The implication is of course intended. If one is "well clear" by 20,000 feet there is no need to take avoiding action!


text:
How does the FOVE system work with the Airbus FMS?
The Flight Operations Versatile Environment (FOVE) is a separate software system used with Airbus aircraft by dispatchers to determine performance data to enter into the FMS. There seems to be little info on the interwebs about it.
Since the FMS takes the parameters and makes its own calculations, I'm not sure why a separate system is needed. A U.K. CAA bulletin says:

"As [FOVE] gives more accurate performance figures it is generally used on occasions where takeoff performance is more limiting."

In what way does it produce more accurate figures than the aircraft's own FMS? Is FOVE created by Airbus or a third party? If it's third party, has Airbus approved it?
How does FOVE work with the FMS? Do they just override the FMS calculations, or does it give them alternate data to enter into the FMS to create the required parameters?

The FOVE system as described in your reference is a computer program to calculate takeoff performance parameters (simplified: limit weights and associated thrust and speeds) which the FMS is not able to do by itself for a variety of reasons, most notably lack of processing power and storage size.
The FOVE outputs are then manually entered into the FMS to serve as inputs/targets/limits during takeoff.
Other options of deriving the same data are looking them up in manufacturer or operator created data tables (the Performance Manual in your reference) or graphs or using an electronic means of computation e.g. in an Electronic Flight Bag on the flight deck.
I'm not sure whether FOVE is an Airbus-provided software or created by the operator or a third party. There are other, similar software solutions by a variety of companies including Airbus and Boeing for their product lines.
Common to all of them is that in order for them to be permitted for EASA and FAA operations, they will have to be based on certified performance data provided by the manufacturer.
As my answer is very general, I have not provided references for my musings at this point. If useful, I might be able to dig out some links for further reading in the (European) morning.


text:
What is the EASA definition of night time?
EASA requires pilots to log separately night time and night landings in the personal logbook. Now, I'm not sure in which period of time a landing is a night landing and flight time is night flight time. I would appreciate your answer, maybe also with a trustworthy source.

According to this handy document from EASA, night is defined as:

…the period between the end of evening civil twilight and the beginning of morning civil twilight, or such other period between sunset and sunrise as may be prescribed by the appropriate authority, as defined by the Member State.

(The FAA and ICAO use a similar definition.)

You can get the Civil Twilight times from a convenient astronomical calendar, but ignoring the specifics, the same rule of thumb the FAA uses for purposes of night currency will likely work for you too:

Night starts one hour after sunset
(Sunset being when the last of the visible sun disc drops below the horizon.)
Night ends one hour before sunrise
(Sunrise being when the first of the visible sun disk breaks the horizon.)

This actually cheats you out of a few minutes of "night" on either side of the calculation, but it's conservative guidance if you're conservative in what you log you won't accidentally mess up and give yourself more night time than you're really entitled too (i.e. you won't make yourself "night current" when you really aren't).

Note that I'm a US pilot -- since all my flying and training is based on FAA regs in the US if I'm completely off the mark and any European pilots or CFIs want to set me right it would be much appreciated :-)

I don't know about the rest of Europe, but at least Germany defines night as sunset+30 minutes to sunrise-30 minutes, so not a full hour.

@roe In that's probably about what "Civil Twilight" works out to be (the length of Civil Twilight varies a bit by location and season, but 30-40 minutes either side of the sun seems about right for most of Germany)

Yeah, I guess I was referring to the "... or such other period between sunset and sunrise as may be prescribed by the appropriate authority" part. An interesting side note, I'm not 100% sure of this, but I think they also redefine sunset/sunrise for the entire country to be at the latitude of the city Kassel (longitude still matters though). It works out to a couple of minutes at most, but still wonky.

And for those who, like me, didn't know what civil twilight is and had to look it up, it's when the center of the sun is below the horizon, but no further than 6 degrees. So depending on where (latitude) you are, the duration will be different.

Civil twilight is defined in astronomy as the two periods of day in the morning and in the evening when the Sun's top is between 0 and -6 degrees below the horizon. This can vary between something like 30 minutes and an hour at 45 latitude (I'm not sure about the exact numbers). The term "night" used here therefore corresponds to the "civil night". The "astronomical night" is defined in the same way, but the value is -18 rather than -6. It means that for example in Oulu summertime, nothing counts as night :) (Oh I see that this is what @falstro says, I just add more details).

Sunset being when the last of the visible sun disc drops below the horizon. Won't you be losing night time by flying west at sunset? The sun sets a fair bit later at FL300 than it does at ground level. Same holds true flying west at sunrise.

As of today (5 June 2023) in London, the difference between sunset and evening civil twilight is 44 minutes. So 30 minutes is not sufficient. An hour is conservative, but ideally you'd just google the civil twilight times for each day.

For europe the night is defined in the standardized european rules of the air (SERA, VO(EU) 923-2012) in the following way:
‘night’ means the hours between the end of evening civil twilight and the beginning of morning civil twilight. Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the morning when the centre of the sun’s disc is 6 degrees below the horizon
You will find the latest version of SERA here:
http://eur-lex.europa.eu/homepage.html
SERA definition is consistent with ICAO definition found in Annex 6 Part I:
Night. The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period
between sunset and sunrise, as may be prescribed by the appropriate authority.
Note.— Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in
the morning when the centre of the sun’s disc is 6 degrees below the horizon.

CAP393 UK In paragraph (5) confirms "night time" as 30 minutes after sunset to 30 minutes before sunrise.

As another comment to a similar answer already says, there are a number of definitions of sunset/sunrise, but your answer doesn't specify which.

Sunset is defined as the point where the upper limb of the sun drops below the horizon and is a defined astronomical term. The other answers refer to civil twilight, not sunset. There should not be any confusion between sunset & the various forms of twilight.

As of 2021, CAP393 does not define "night", no mention of sunrise/sunset or twilight.

CAP393 UK In paragraph (5) ‘day’ means the time from half an hour before sunrise until half
an hour after sunset (both times exclusive), sunset and sunrise being
determined at surface level.

there are a number of definitions of sunset/sunrise, but your answer doesn't specify which.

"being determined at surface level" seems to add some specificity, but there are no other astronomical definitions of sunset, just three sorts of twilight ...

As of 2021, CAP393 does not define "night", no mention of sunrise/sunset or twilight.


text:
What are the benefits of a 'cranked arrow' delta wing?
What are the benefits of the 'cranked arrow' delta wing that was used on the variant of the F-16, the F-16XL?

Sourceenter link description here

The goal of the cranked arrow was to have a high sweep inboard panel for low drag at supersonic speeds, and a low sweep outboard panel to provide better handling and maneuverability at subsonic speeds.[citation needed] (from Wikipedia)

Totally agree with @RalphJ, voting to not close.

There are a few reasons for choosing the cranked delta wing, as used in F-16 XL. The main one is to maintain comparable performances in the supersonic and sub/transonic speeds- a reason similar to the variable geometry wings, like one used in F-111, with the same disadvantages. According to NASA,

The  new  wing, common for both the -1 and -2 versions, was designed to provide the F-16 aircraft with improved supersonic performance while   maintaining comparable transonic performance to that provided by the current F-16 design.

Basically, you want to have good performance in the subsonic regime- improving the low speed handling and acceptable landing characteristics (the delta wings are not exactly known for that) and in supersonic regime- low aspect ratio and low drag. The result is a compromise, which is more often than not, more trouble than it is worth. From this paper:

When compared to a delta wing, a double delta wing and cranked arrow   wing planforms indicate higher aerodynamic performance and maneuverability at high angles of attack,  because  a vortex  generated  from  the  strake  wing  (or  the  inboard  wing) stabilizes the flow on the main  wing  (or  the  outboard  ing) .. . furthermore, the outboard wing  leading-edge that has smaller sweepback angle than that of the inboard wing increases the wing aspect ratio as a whole and low-speed performance is improved.

Another issue with the cranked delta wings is its tendency to pitch up at high angles of attack.

The main benefits are:

High root thickness, so the wing can be made stiffer and stronger where the loads are highest.
Better pitch stability in the post-stall region, so no AoA limit needs to be observed. The X-31 could maneuver with thrust vectoring only because its cranked arrow delta wing was more or less neutral in pitch over the full AoA range. A simple delta wing produces strong pitch-up moments in the post-stall region wich would quickly overpower the moments possible with thrust vectoring.


text:
What is the typical blade pitch angle of a ram air turbine?
I'm building a simple 3d model of one and because reasons I won't be able to give it a variable blade pitch so I need to find a typical value. My google-fu has failed me so far on this.

A Radial air turbine? A radial turbine in a turboshaft, or a propeller-like Ram Air Turbine such as deployed by the A320 if all power fails?

@Koyovis sorry meant to say ram air turbine

Ram Air Turbines have variable pitch which is set according to demanded load and airspeed, and the controller keeps the rotational speed as high as possible for maximum efficiency. Typical operational RPM of a RAT is between 5500 and 7700 rpm, at speeds between 125 - 375 knots. Let's take the averages: 6600 RPM @ 250 knots = 700 rad/s @ 130 m/s.
At a disk diameter of 1 m and a spinner diameter of 20 cm, lets look at velocity triangles at the blade root, centre and tip:

Blade root: R = 0.1 m, rotational speed $V_{rot}$ = 0.1 * 700 = 70 m/s. With incoming air at 130 m/s, this creates a local velocity pitch angle of arctan (130/70) = 62 deg
Blade centre: R = 0.3, $V_{rot}$ = 0.3 * 700 = 210 m/s, velocity pitch angle = arctan (130/210) = 32 deg.
Blade tip: R = 0.5, $V_{rot}$ = 0.5 * 700 = 350 m/s, velocity pitch angle = arctan (130/350) = 20 deg.

Note that these are unloaded velocity triangles, the blades can only generate power with air coming in at a local angle of attack. We're rough estimating, so you could take a pitch of 25 deg at tip, 35 at centre, and linearly twist onto 45 deg at root (most of the power is generated at the outer part of the blade).


text:
What are the EU-equivalent terms of the FAA ATC tower, TRACON, and center in radio calls?
Does ATC in the EU have equivalents to the US FAA tower, TRACON, and center facilities? What are they called?

This is too broad @jeff0000.

Related, but as you can see from that question (and others linked to it) this is probably a very broad question. If you're asking about the specific equivalents of Tower, Approach and Center then you might re-word your question to focus on that.

Area control centre   CONTROL
Approach control    APPROACH
Approach control radar arrivals ARRIVAL
Approach control radar departures   DEPARTURE
Aerodrome control   TOWER
Surface movement control     GROUND
Radar (in general)  RADAR
Precision approach radar   PRECISION
Direction- finding station HOMER
Flight information service INFORMATION
Clearance delivery DELIVERY
Apron service APRON
Company dispatch DISPATCH
Aeronautical station RADIO
Aerodrome Flight Information Service AFIS
Heliport Information Service HIS


text:
Symbology on standard terminal arrival (STAR) charts: T-ended vs arrow-ended lines?
I was looking at the STARs at KPHX. The ARLIN FOUR arrival here has T-ended lines between the BLYTHE VOR and SCOLE, and between SCOLE and CALIE fixes. It also has arrow-ended lines between CALIE and HYDRR, and between HYDRR and PAYINT.
What does the difference in symbology mean?
At first I thought it indicated a different MEA, but then I looked at the DSERT TWO arrival here, and I see the T-ended lines between SHOCK and BUSTD, and between BUSTD and YOLOW, and the MEAs on both the neighboring segments is the same (9000).

404 (not found) on both your links currently.

According to the FAA Chart User's Guide, the arrows are transition routes and the 'T' is "Altitude change at other than Radio Aids." So your original assumption is correct.
Regarding DSERT TWO ARRIVAL and BUSTD. You are correct that the altitude doesn't change at BUSTD when proceeding to YOLOW, but it does change (9000 to 8000) when proceeding to BAYTA. That is why there is a 'T' at BUSTD.

A thin line (without a radial value) is a transition, a thick line is the main route.


text:
What is the ICAO code and callsign for Amazon Prime planes?
Looks like Amazon started flying its own planes to transport goods - check out the announcement here. Apparently they've been flying since at least August 2016, and I just found out about it now, lol.
This is their promo video.
Anyone know what their three letter ICAO code and their callsign is?
Edit: Looks like CNBC confirms that Atlas Air operates flights for Amazon in this crash. There may be others.

As best I can tell, Amazon Air does not hold its own air carrier certificate; they contract with cargo airlines to operate their flights. Per Wikipedia, those contractors are Air Transport International, ABX Air, and Atlas Air. These operators then use their own callsigns.
For example, the aircraft shown in your first link, N1997A ("Amazon One"), is apparently owned  by Titan Aviation, dry leased to Amazon Air, and then operated by a Titan sister company: Atlas Air. The aircraft bears the legend "Operated by Atlas Air Inc" on the paint job. So for the flight it happens to be flying to Charlotte at this moment, it would be identified as GIANT 3581, "Giant" being the codesign for all of Atlas' operations.
But another aircraft in their fleet, N331AZ, is contracted to Air Transport International, and uses the creative callsign "AIR TRANSPORT."
So they don't have an ICAO code or callsign; the companies they hire to operate their flights do.

I was listening to PDX tower and watching flights on FlightRadar24 one night when I heard the tower and then departure talking to a commercial jet with a very strange (to me) call sign (Giant, I'm pretty sure). FlightRadar identified the aircraft (same flight number) as an Amazon 767.
I found the same flight on the app tonight by searching out Atlas Air and the photo link (via reg number) shows the Prime livery. So it sounds like just about everyone here is right in some sense.
Ric


text:
If you're flying VFR in controlled airspace and in contact with ATC, do you need permission to change altitudes?
I think the controller sometimes gives altitudes for VFR traffic to fly, but do pilots actually need permission to change their altitude?

Which country or regulations are you asking about?

The US, thanks.

In Bravo, where you are cleared in, and the area is large, I would say yes.
In Charlie or Delta, it would depend on how much other traffic was around.

The question should NOT be marked as a duplicate: you should have a clearance in a controlled airspace (except E for VFR) regardless of whether you requested flight following or not. But the answer is really pretty much the same as during the flight following: it depends on airspace class and ATC instructions, and you should always follow ATC instructions.


text:
Is a hold short expected when given taxi directions to a runway?
When a ground controller gives taxi instructions to a runway, are pilots expected to hold short by default if an explicit instruction to hold short isn't given?

Yes.  A taxi clearance enables you to taxi an aircraft through a controlled movement area within the terms of the clearance given by ground control.  Entering an active runway requires an explicit and separate clearance from the tower to do so.
In addition, crossing any runway which intersects your taxi path requires an explicit clearance from ground control to do so.  This clearance can be included in the original taxi clearance or a separate clearance wile your aircraft is currently taxiing.  If you reach the hold lines of an intersecting runway, you must hold short unti you are cleared to cross by ground control.

Yes.  Only when the taxi instruction would require the pilot to cross another runway on the way to the one he/she is cleared to, is the controller required to explicitly tell you whether to hold short, or cleared to cross, the intervening runway. And, in either case, the Pilot In Command is required to repeat back that portion of the taxi instructions verbatim.


text:
How can I overlay a VFR sectional on another map to identify features and landmarks?
How do I know which highways and landmarks on a VFR sectional align with which real-world features? Is there a way to overlay the VFR sectional map from the FAA on top of Google Maps or Bing?
Edit: I'm asking in relation to VFR flight in general where you are responsible for your own navigation, and not about a specific route of flight.

Do you happen have any particular problem with any area? Or you just want to have a general idea how is it done?

@vasin1987 Now that I think about it, both. To be specific, I'm having problems with Hawthorne, Santa Monica, and John Wayne (including that pesky permanent Disneyland TFR). What's the process in general?

I don't remember details, but I have used overlays of VFR sectional charts in Google Earth

Seems to me you're going to be directed by SoCal approach that whole route per the routing shown in Skyvector.com, especially with the LAX Class B right there, and the TFR will be the last of your worries. Put your enroute and the final destination into your GPS (Foreflight or whatever), and be ready for deviations.

Thanks. I'm actually asking in a more general context of being on a VFR flight where you are responsible for your own navigation, and not about being on a specific route. I mentioned examples of specific airspace, but didn't mean to imply a particular route between them.

Well, if VFR on your own, the sectional is your friend. It has the useful shown. I don't think you'll be on your own flying around LAX. ATC is there to help you out, use them.  Looking at maps.google.com centered around Hawthorne, CA, there are so many  highways it would be hard to pick one or two out follow them without many hours flying over to recognize things.  GPS with headings & distance (or moving map display) will really save your butt there.

True, use ATC if available, but it's busy airspace and they don't always have time to give you vectors, or you might not be able to get a word in on the radio. GPS units can also fail. A (good) pilot should be able to navigate comfortably without a GPS and only with VFR landmarks. GPS can be used if available.

Hope you know your local landmarks! Scooting along at 2000 ft and 2500 ft, you'll certainly get a good view of them.


text:
Does the ICAO definition of an "aircraft" include a minimum altitude capability?
The German air law includes in their legal definition of a "Luftfahrzeug", which is the equivalent of an aircraft, other devices intended to operate in the airspace if they are capable of being operated more than 30 meters (100 ft) above ground or sea level.
Does an equivalent to this 100 ft threshold exist in ICAO documents or other international regulations? If yes, where?
The background of my question is: if an unmanned aircraft has a technical feature preventing it from flying above 100 ft, would it still qualify as an aircraft and would all regulations about aircraft apply?
I would also like to know, why the 100 ft threshold was put into the German (or other) laws. I could image that it was intended to exclude wing in ground effect crafts from the aircraft category. Is a wing in ground effect craft an aircraft according to ICAO definition?

Is there a lower altitude threshold in the ICAO definition of an aircraft?
No.
Is a wing in ground effect craft an aircraft according to ICAO definition?
No.

I believe the ICAO is based on the Chicago Convention
The 2006 9th edition begins

THEREFORE, the undersigned governments having agreed on
  certain principles and arrangements in order that international
  civil aviation may be developed in a safe and orderly manner
  and that international air transport services may be established
  on  the basis of equality of opportunity and operated  soundly
  and economically

Although this has a section on definitions, it doesn't define aircraft.
The ICAO ADREP taxonomy contains this definition:

Aircraft. Any machine that can derive support in the atmosphere from the reactions of the air
  other than the reactions of the air against the earth's surface. (Annex
  8)

That appears to exclude vehicles whose support relies on ground effect only.

Why [was] the 100 ft threshold [...] put into the German (or other) laws?
That might be better answered in law.se


text:
Is there a database of European surveillance radar installations?
Does anybody know a link to a database or appropriate webpage where I can find the locations of surveillance radar installations in Europe?

I somehow suspect this to be non public information.

@Federico You can find such data for US data on the web. Europe may be different, though.

Do you think about some particular kind of radar? Surveillance wording appears in primary and secondary "surveillance radar" (PSR / SSR). PSR is the true echo radar (some are military), SSR is a transponder interrogator. You probably need to look at each country individually, e.g. for France you have civil PSR and SSR on pages 19/20 of this non authoritative document.

Thanks for the link. If available, i would be interested in the coordinates of both, PSR and SSR, civil as well as military. The purpose will be to use the data in simulation for radar coverage and frequency usage. For germany i found an official document here.

Meanwhile i found an answer to my question. Location data of radar stations is for most countries provided in the AIP ENR chapter 1.6 "ATS Surveillance Services and Procedures". Some countries do not provide the coordinates of radar location, but only a coverage map. European AIP may be accessed through Eurocontrols EAD service.


text:
What are the empty weight and maximum takeoff weight of the Moller Skycar?
I know what are empty weight and MTOW, which are data I need for my school project. But the website for Moller Skycar only shows the gross weight and net payload: https://www.moller.com/moller_skycar400.html.
But in the wiki for the same vehicle, it shows that the empty weight is the gross weight and the MTOW is the gross weight + net payload: https://en.wikipedia.org/wiki/Moller_M400_Skycar.
Could you guys please help me figure out what is the correct value for the Moller Skycar 400?

Considering that the whole project is basically vaporware, I wouldn't put much stock in ANY number. That said, "gross weight" is basically a "right now" value (the GW of this aircraft right now is ___), while MTOW is a limitation, and empty weight is (generally) a constant. If max payload + empty weight = MTOW, then they're including the weight of the fuel as part of "payload" (ummm, okaaaay...), or else somebody neglected the weight of the fuel. Since it's basically a bankrupt fantasy, who really knows at this point?

Yep.  Vaporware... love that term. It's so perfectly descriptive.

Wikipedia is a joke; it's a shame when questions center on it.

First of all, Wikipedia does not regard itself as a reliable source, and nor should you. It is only as reliable as the last editor, and since it is the encyclopedia that "anyone can edit" (and frequently does, me included :-) ), that is not saying much. In fact the last editor to touch those stats has messed it up and the stats given do not match the sources cited.
An aircraft's gross weight is the weight of the plane and everything on board. Typically the maximum gross weight is also the maximum takeoff weight (MTOW), although a few planes can take on extra fuel when airborne so that their gross weight then exceeds the MTOW.
As stated in another answer, the M400 is just a recurrent daydream and all figures are estimates provided by the daydreamer. But, with that in mind, the daydreamer's own numbers are clearly the definitive daydream. In other words, go with the website.

Moller managed to get multiple prototypes into hover, the last one being the version with four nacelles and little stubby wings that was to be self-piloting (i.e. operator wouldn't need a pilot's license).  His operating mode very strongly resembled the new wave of passenger drones, he just had the misfortune of being fifty years ahead of the technology.

He was my manufacturing methods instructor at UC Davis in 1974. His earlier flying car designs were suspended from the ceiling of the fluid dynamics lab where the wind tunnels were located. When not teaching in the ME department he ran a small company called DiscoJet that manufactured spark arrestor mufflers for use on off-road motorcycles.


text:
Do I have to follow airways to meet the IFR cross country 250 NM flight requirement in 61.65?
I understand that there is cross-country flight of "a distance of at least 250 nm along airways or ATC-directed routing" requirement for the IFR rating, but I'm not sure if understand what the second part of that sentence means.
Do I have to follow Victor airways? Will obtaining flight following from ATC be sufficient?

14 CFR 61.65(d)(2) says:

(ii) Instrument flight training on cross country flight procedures,
  including one cross country flight in an airplane with an authorized
  instructor, that is performed under instrument flight rules, when a
  flight plan has been filed with an air traffic control facility, and
  that involves—
(A) A flight of 250 nautical miles along airways or by directed
  routing from an air traffic control facility;
(B) An instrument approach at each airport; and
(C) Three different kinds of approaches with the use of navigation
  systems.

The wording is saying that you must follow airways or a route given by ATC. But since the flight must be under IFR, you'll get a route from ATC in your clearance anyway so I don't know why the FAA has the airways reference in there.
(As a complete guess it may be left over from a time when there was less radar coverage and the FAA wanted to make sure that instructors weren't taking any shortcuts.)
I don't know what flight following has to do with this because that's VFR, and the flight must be IFR.

OK. I guess, I didn't noticed that (A) is a subsection of (ii). I thought I can use one of my VFR long x-country to satisfy this req. I guess, not... I do have to pay the instructor for this, too... oh, well.

@Pondlife Don't you think that it means the flight needs to be planned on published airways, but it is simply giving the exception that if ATC needs to deviate you it won't bust your ability to count the flight for the rating?  A pilot's choice to file RNAV does not default it to being ATC-directed simply because they approve your plan with a clearance, therefore the default is along airways to meet this requirement. Just my opinion.

@RyanMortensen I see what you mean but I read it as "airways or ATC". I believe the key word is "or" because that means that either option meets the requirement. I'll dig some more when I have more time, though.

@Pondlife I see what you're saying there.  If I think of it that way though, then it's also possible that it could be interpreted as published airways or ATC vectors, but not RNAV.

@RyanMortensen "Cleared direct KABC" is ATC-directed routing, so RNAV is fine. Flying RNAV in class G (where that is still possible) is not, unless along an airway.

It must be under IFR, so flight following is not an option.
You don't have to follow airways as long as you're following a route as directed by ATC. Radar vectors, random RNAV routes, and airways are all options. VFR-on-top and undirected IFR flight in class G are not. The latter is not really possible in the US anymore anyway, but it is possible elsewhere and there is no regulation that says your flights need to be done in the US.

No, you must file a flight plan, and fly the route you are cleared to, or as directed by ATC (such as for traffic clearance).


text:
Will I have to do a checkout ride at a rental place if I'm already familiar with the aircraft type?
I've done my training and checkride on Piper Archer (PA-28A). Will a rental place make me take an checkout ride with an instructor if I wanted to rent the same plane model?

Are you renting the plane from a different place than you did the training with? Then most likely yes if you don't have a relationship with the new place yet.

Are you asking about a specific country? I suspect it won't change the answer much but it would help to be clear, in case there are any regulations involved.

Generally they will make you do a checkout with their own instructor, at least this is the situation I have always encountered when renting from various places. Generally speaking, when you go to a new rental place they will audit your log book, put you in their system and make you fly with one of their instructors for a few reasons:

While your license was issued, presumably legitimately and your log book may be full of hours that are presumed to have occurred they still want to make sure you can do what you say you can.
Generally their insurance will require it. At least this is what I have always been told by FBO's/Flight Schools. Both of the places I fly out of, even require a recurrent 90 day checkup with an instructor to be able to keep renting (no matter how much you fly).

One thing to note is that none of these are FAA regulations, so you are legal to fly the PA-28 as long as you have your bi-annual and TO/LD requirements filled. The rental shops can how ever impose other rules as they see fit (mine does not allow flights to grass strips with the rental planes).
Note: some rental shops may also have differing gap policies on their insurance. It's worth asking about this up front and seeing if you need to carry any gap insurance.

Excellent answer. Thank you very much.